pgsql: Remove ancient special case code for dropping oid columns

Remove ancient special case code for dropping oid columns

The special handling of negative attribute numbers in
RemoveAttributeById() was introduced to support SET WITHOUT OIDS
(commit 24614a9880). But that feature doesn't exist anymore, so we
can revert to the previous, simpler version.

Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: /messages/by-id/52a125e4-ff9a-95f5-9f61-b87cf447e4da@eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7ef2912519fdea0dd0f6747c4dc008c99dc51e90

Modified Files
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src/backend/catalog/heap.c | 99 ++++++++++++++++++++--------------------------
1 file changed, 43 insertions(+), 56 deletions(-)